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| Images of freshly caught pacus highlighting groups with significant intraspecific genetic diversity: (a) Myloplus arnoldi, Tapajόs River; (b) M. arnoldi, Nhamundá River; (c) Myloplus asterias, Branco River; (d) M. asterias, Nhamundá River; (e) Myloplus schomburgkii, Nhamundá River; and (f) M. schomburgkii, Tapajόs River.
All images were taken by the authors.
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Piranhas and pacus (Characiformes: Serrasalmidae) are a charismatic but understudied family of Neotropical fishes. Here, we analyse a DNA barcode dataset comprising 1,122 specimens, 69 species, 16 genera, 208 localities, and 34 major river drainages in order to make an inventory of diversity and to highlight taxa and biogeographic areas worthy of further sampling efort and conservation protection. Using four methods of species discovery—incorporating both tree and distance based techniques—we report between 76 and 99 species-like clusters, i.e. between 20% and 33% of a priori identifed taxonomic species were represented by more than one mtDNA lineage. There was a high degree of congruence between clusters, with 60% supported by three or four methods. Pacus of the genus Myloplus exhibited the most intraspecifc variation, with six of the 13 species sampled found to have multiple lineages. Conversely, piranhas of the Serrasalmus rhombeus group proved difcult to delimit with these methods due to genetic similarity and polyphyly. Overall, our results recognise substantially underestimated diversity in the serrasalmids, and emphasise the Guiana and Brazilian Shield rivers as biogeographically important areas with multiple cases of across-shield and withinshield diversifcations. We additionally highlight the distinctiveness and complex phylogeographic history of rheophilic taxa in particular, and suggest multiple colonisations of these habitats by diferent serrasalmid lineages.
Valeria N. Machado, Rupert A. Collins, Rafaela P. Ota, Marcelo C. Andrade, Izeni P. Farias and Tomas Hrbek. 2018. One Thousand DNA Barcodes of Piranhas and Pacus Reveal Geographic Structure and Unrecognised Diversity in the Amazon. Scientific Reports. 8:8387. DOI: 10.1038/s41598-018-26550-x
